Optical element supporting device in an apparatus for recording reproducing information

ABSTRACT

An optical element supporting device has one ends of two parallel plate springs, which are extended in a tangential direction, fixed to a holder, has the other ends thereof fixed to a fixture member, and has a collimator lens locked in an opening of the holder. A base fixed to the bottom of the fixture member has two yokes formed thereon. Magnets each polarized in two directions are fixed to the insides of the yokes. Coils are fixed to two surfaces of the holder opposed to the magnets. A target is fixed to the holder, and a sensor is fixed to the bottom of the base. When a current flows into the coils, electromagnetic force is produced along an optical axis due to the interaction between the coils and the magnets opposed to the coils. This causes the parallel plate springs to loosen. Consequently, the holder, target, collimator lens, and coils move as a whole along the optical axis.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical element supportingdevice for information recording/reproducing apparatuses. The opticalelement supporting device supports an optical element included in aninformation recording and/or reproducing apparatus for recording and/orreproducing information in or from a recording medium, for example, amagnetooptical disk, a write-once optical disk, a phase change opticaldisk, a CD-ROM, a digital video disk (DVD), or an optical card.

[0003] 2. Description of the Related Art

[0004] In recent years, a three-dimensional optical recording medium hascome to light as one of promising super high-recording density opticalrecording media that are of a new generation succeeding the generationof such optical recording media as a magnetooptical disk, a write-onlydisk, a phase change disk, a CD-ROM, a DVD, and an optical card.

[0005] The conventional optical recording media are designed to haveinformation recorded two-dimensionally on a recording layer. Incontrast, when it comes to the three-dimensional optical recordingmedium, information is not only recorded two-dimensionally (on a planarbasis) on a recording layer whose thickness is larger than a depth offocus offered by a laser employed, but also recorded in the depthdirection of the recording layer. Therefore, if information is recordedon one hundred strata in the depth direction in the three-dimensionalrecording medium, a recording density that is one hundred times largerthan a currently available recording density can be attained readily.

[0006] Study reports on such a three-dimensional optical recordingmedium have been carried in, for example, a collection of notes(P.39-P.40) prepared for lectures given at the 1992 Symposium of theAssociation of Optics in Kyoto or a collection of notes (29p-B-11 and29p-B-12) prepared for lectures given at the 40th Meeting of the JapanSociety of Applied Physics and Related Societies. However, the reportedrecording media are not intended to record or reproduce information inthe form of a disk.

[0007] Moreover, for example, Japanese Unexamined Patent Publication No.4-301226 has described an information recording/reproducing apparatusfor recording and/or reproducing information in or from a disk-likeoptical recording medium having a guiding surface and a plurality ofrecording surfaces.

[0008] According to the prior art, two beams are employed; that is, aguiding beam to be irradiated to the guiding surface and a scanning beamto be irradiated to the plurality of recording surfaces. Two spots ofthe beams formed on the optical recording medium are advanced in adirection orthogonal to a direction of focus. Thus, the scanning beam isguided and information is recorded or reproduced. The guiding beam ispositioned on a guiding track, while the scanning beam is positioned ona recording track on any of the plurality of recording surfaces.

[0009] Since the scanning beam must be positioned on any of theplurality of recording surfaces, the prior art employs adirection-of-optical axis shifter 104 composed of, as shown in FIG. 14,lenses 101 and 102 and a correcting element 103. Specifically, the lens102 is moved along an optical axis in order to control the position ofthe scanning beam relative to the guiding beam in the direction of theoptical axis.

[0010] Furthermore, the aforesaid patent publication has described anapparatus for recording or reproducing information by positioning alight spot on each of multiple recording layers of an optical recordingmedium. When this kind of optical recording medium is used formultilayer recording, the lens 102 is moved along an optical axis of anoptical system including the lens to a position optimal for eachrecording apparatus. Assume that the focal length of an objective lensthrough which light forming a spot is irradiated to the opticalrecording medium is 3 mm and the focal length of the lens is 12 mm. Inthis case, an interlayer space between adjoining ones of the multiplerecording layers shall be 10 μm and the number of multiple recordinglayers shall be ten. For causing the light spot to sweep the ten layers,the lens must be moved a length calculated as 9 layers×10μm×(12/3)²=1440 μm.

[0011] As a supporting device for the lens 102, a device for supportingthe lens using two parallel cantilevered plate springs is generallyadopted. When this kind of supporting device is employed, if the lens ismoved along the optical axis, the springs loosen. This causes a movableassembly to move in a direction in which the springs are extended.Consequently, the lens 102 is displaced perpendicularly to the opticaxis of the lens 101 in the direction of extension of the springs. Theray axis of light emitted from the lens 102 slopes in the direction ofextension of the springs. This poses a problem in that the position ofthe scanning beam relative the guiding beam on a recording medium ischanged in a direction orthogonal to the ray axis of the scanning beam.

[0012] For minimizing the change in the relative position, the springsshould have a sufficiently large length. However, this leads to anincrease in the size of the supporting device.

SUMMARY OF THE INVENTION

[0013] An object of the present invention is to provide an opticalelement supporting device for information recording/reproducingapparatuses. The optical element supporting device is designed so thatwhen an optical element is moved, even if the relative positions of twolight spots formed through an objective lens are changed in a directionparallel to a direction of focus, a deviation of one of the light spotsfrom the other light spot in a direction of tracking can be minimized.

[0014] According to the present invention, an optical element supportingdevice for information recording/reproducing apparatuses consists mainlyof a light source, an objective lens, an optical element, and a supportmember. The light source irradiates a light beam. The light beamirradiated from the light source forms at least one light spot on arecording medium after passing through the objective lens. The opticalelement routes the light beam irradiated from the light source to theobjective lens. The supporting member supports the optical element sothat the optical element can move in a first direction. The supportingmember is extended so that when the optical element is moved in thefirst direction, the position of the light spot in a direction of focuswill be changed, and the light spot will travel in a directionsubstantially parallel to the recording tracks of the recording medium.

[0015] Other features and advantages of the present invention will beapparent from the description below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows an arrangement of optical elements constituting anoptical system included in an information recording/reproducingapparatus in accordance with an embodiment of the present invention;

[0017]FIG. 2 shows an arrangement of major optical elements of theoptical system shown in FIG. 1;

[0018]FIG. 3 shows the structure of a disk shown in FIG. 1;

[0019]FIG. 4 shows an appearance of a supporting drive unit shown inFIG. 1;

[0020]FIG. 5 is an exploded view showing the components of thesupporting drive unit shown in FIG. 1;

[0021]FIG. 6 is a sectional view showing a section cut along the opticalaxis of a guiding optical system included in the supporting drive unitshown in FIG. 4;

[0022]FIG. 7 is a sectional view showing a section cut perpendicularlyto the optical axis of the guiding optical system included in thesupporting drive unit shown in FIG. 4;

[0023]FIG. 8 is an explanatory diagram concerning the operation of asensor shown in FIG. 4;

[0024]FIG. 9 is the first explanatory diagram concerning the operationof the supporting drive unit shown in FIG. 4;

[0025]FIG. 10 is the second explanatory diagram concerning the operationof the supporting drive unit shown in FIG. 4;

[0026]FIG. 11 shows an arrangement of optical elements constituting afirst variant of the optical system included in the informationrecording/reproducing apparatus shown in FIG. 1;

[0027]FIG. 12 shows an arrangement of optical elements constituting asecond variant of the optical system included in the informationrecording/reproducing apparatus shown in FIG. 1;

[0028]FIG. 13 shows an arrangement of optical elements constituting athird variant of the optical system included in the informationrecording/reproducing apparatus shown in FIG. 1; and

[0029]FIG. 14 shows the components of a conventionaldirection-of-optical axis shifter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Referring to the drawings, an embodiment of the present inventionwill be described below.

[0031] (Constituent Features)

[0032] As shown in FIG. 1, in an information recording/reproducingapparatus, light emitted from a laser diode (LD) 1 and used to record orreproduce information is light linearly polarized perpendicularly to thesheet of FIG. 1 and collimated by a collimator lens 2. The lightcollimated by the collimator lens 2 falls on a beam splitter (halfmirror) 3. Part of the light is transmitted and the other part thereofis reflected. Light transmitted by the beam splitter 3 is converged at acondenser 4 and routed to a monitor photodiode (PD) 5. The monitorphotodiode 5 is used to measure an amount of light emitted from thelaser diode 1.

[0033] Moreover, light reflected from the beam splitter 3 is reflectedfrom a polarization beam splitter (PBS) 6 and routed to a mirror 7.

[0034] The light reflected from the beam splitter 3 is, as shown in FIG.2, reflected from the mirror 7 and converged at an objective lens 8.Consequently, a spot P1 is formed in a recording layer of a disk 9.

[0035] Light reflected from the spot P1 reversely traces the foregoinglight path for incidence and falls on the beam splitter 3. Lighttransmitted by the beam splitter 3 is, as shown in FIG. 1, convertedinto converged light, which has undergone astigmatism, by a toric lens(a convex lens plus a cylindrical lens) 11, and then routed to aphotodiode 12. The photodiode 12 has a quartered receiving surface andis used to detect a focus error signal and a recording/reproducingsignal in the recording/reproducing light forming the spot P1 byutilizing astigmatism.

[0036] As shown in FIG. 1, light emitted from a laser diode 13 foremitting guiding light is light linearly polarized parallel to the sheetof FIG. 1. The light is transmitted by a hologram 14, collimated by acollimator lens 15, and transmitted by the polarization beam splitter(PBS) 6. The light is then, as shown in FIG. 2, reflected from thereflecting mirror 7 and converged at the objective lens 8. Consequently,a spot P2 is formed on a guiding surface 16 of the disk 9.

[0037] Incidentally, the collimator lens 15 can be, as shown in FIG. 1,moved along an optical axis of an optical system including thecollimator lens using a supporting/driving means. A sensor 17 detectsthe position of the collimator lens 15 along the optical axis. Thesupporting/driving means consists of two parallel springs, which supportthe collimator lens 15 so that the collimator lens 15 can move along anoptical axis, and a supporting drive unit 50 including coils andmagnets. The supporting drive unit 50 will be detailed later.

[0038] As shown in FIG. 2, the optical axis 18 of a guiding opticalsystem has a slope θ with respect to the optical axis 19 of arecording/reproducing optical system. The spot P2 of guiding light istherefore formed while being separated by a predetermined distance afrom the spot P1 of recording/reproducing light in a direction oftracking (a direction perpendicular to the recording tracks). Thedistance a ranges, for example, from 5 μm to 100 μm.

[0039] Light reflected from the spot P2 is, as shown in FIG. 1,diffracted by the hologram 14 after reversely tracing the light path forincident light. The plus or minus first-order light of the reflectedlight that is diffracted falls on photodiodes 20 a and 20 b each havinga receiving surface that is segmented into six portions. The plus orminus first-order light is converged light. The plus or minusfirst-order light is focused ahead of the photodiode 20 a, and the otherfirst-order light is focused behind the photodiode 20 b. The photodiodes20 a and 20 b are used to detect a focus error signal according to aso-called beam size technique, or to detect a tracking error signal or areproducing signal (track number signal) according to a push-pulltechnique.

[0040] As shown in FIG. 2, the recording/reproducing apparatus has asupporting/driving means 21 for moving the objective lens 8. Theobjective lens 8 is moved in two directions, that is, in a direction offocus and a direction of tracking by the supporting/driving means 21.

[0041] As seen from the above description, the direction of polarizationof light emitted from the laser diode 1 and used to record or reproduceinformation is orthogonal to that of light emitted from the laser diode13 and used for guiding. The light emitted from the laser diode 1 andthe light emitted from the laser diode 13 are mixed and then separatedfrom each other by the polarization beam splitter 6. Consequently, bothlight emanating from the laser diode 13 and falling on the photodiode 12and light emanating from the laser diode 1 and falling on thephotodiodes 20 a and 20 b are negligible.

[0042] Moreover, light emanating from the laser diode 1 and lightemanating from the laser diode 13 are separated from each other in adirection perpendicular to the sheet of FIG. 1. This is because theoptical axis 18 of the guiding optical system slopes with respect to theoptical axis 19 of the recording/reproducing optical system. The lightemanating from the laser diode 1 does not fall on the receiving surfacesof the photodiodes 20 a and 20 b. In contrast, the light emanating fromthe laser diode 13 does not fall on the receiving surface of thephotodiode 12. Consequently, the recording/reproducing apparatus havingthe foregoing components can produce a signal less affected with acrosstalk dependent on the photodiodes or a noise.

[0043] As shown in FIG. 3, the disk 9 has a base layer 22 and arecording layer 10 accumulated on the base layer. The base layer 22 hasthe guiding surface 16 and three reference surfaces 23 a, 23 b, and 23c. The guiding surface 16 has tracks 24 that exhibit a high reflectance.

[0044] The three reference surfaces 23 a, 23 b, and 23 c are located onthe inner circumferential side of the disk 1, and separated from theguiding surface 16 in units of a distance d. In other words, thereference surfaces 23 a, 23 b, and 23 c are located at heights d, 2 d,and 3 d above the guiding surface 16. For example, the distance d rangespreferably from 2 to 50 μm, or more preferably from 5 to 15 μm.

[0045] The recording layer 10 has at least one recording surface formedtherein apart from the guiding surface 16. For example, three recordingsurfaces 25 a, 25 b, and 25 c are formed at the same heights as thereference surfaces 23 a, 23 b, and 23 c respectively.

[0046] Next, the supporting drive unit 50 will be described below.

[0047] As shown in FIG. 1, the collimator lens 15 included in thesupporting drive unit 50 is locked in an opening of a holder 51. Twoparallel plate springs 52 have one ends thereof fixed to the holder 51and have the other ends thereof fixed to a fixture member 53. The twoparallel plate springs 52 are extended in a tangential direction.Herein, a direction referred to as the tangential direction is such thatwhen the collimator lens 15 is moved in the direction of extension ofthe plate springs 52, the spot P2 travels on the recording medium in thedirection of a tangent to a track on the recording medium. For example,assuming that the plate springs 52 are extended perpendicularly to thesheet of FIG. 1, when the collimator lens 15 is moved in the directionof extension of the plate springs 52, the spot P2 travels on therecording medium in a direction of tracking. In this case, it is saidthat the plate springs are extended in the direction of tracking.

[0048] As shown in FIG. 4 and FIG. 5, the bottom of the fixture member53 is fixed to a base 54 that is an iron plate. Two yokes 55 are formedon the base 54 so that they will face each other to sandwich the holder51. Magnets 56 each being polarized in two directions are fixed on theinside of the yokes 55. Coils 57 each formed by winding wire about asquare frame are fixed to the two surfaces of the holder 51 opposed tothe magnets 56. The coils 57 are each positioned so that two sidesthereof will lie on two pole faces of each magnet 56. Moreover, a target58 is fixed to a surface of the holder on the opposite side thereofrelative to the laser diode 13. A curved reflecting surface 58 a isformed as an inner surface of the target 58. The target 58 is made of awhite plastic. The face of the target 58 is formed as the reflectingsurface 58 a. Alternatively, the face of the target 58 may be platedwith nickel or the like in order to improve the reflectance exhibited bythe face.

[0049] The sensor 17 is fixed to the bottom of the base 54. The sensor17 has a receiving surface 59 segmented into a plurality of portionsalong the optical axis 18. The reflecting surface 58 a of the target 58is shaped so that light reflected from the reflecting surface 58 a willbe, as shown in FIG. 6, converged at a point on the receiving surface59.

[0050] When a current flows into the coils 57, electromagnetic force isproduced along the optical axis 18 owing to the interaction between thecoils and the magnets 56 opposed to the coils. This causes the springs52 to loosen. Moreover, the holder 51, target 58, collimator lens 15,and coils 57 are moved as a whole along the optical axis 18.

[0051] Light emanating from the laser diode 13 is routed to thecollimator lens 15, substantially collimated, and routed to the target58. As shown in FIG. 7, the target 58 has an opening 58 b shaped like anupper half of a vertically elongated ellipse. For this reason, out oflight emitted from the collimator lens 15, light entering the centralvertically-elongated portion of the opening is not intercepted by thetarget 58, but directed to the objective lens 8. Although the objectivelens 8 is moved in the direction of tracking, light necessary at thattime is reserved.

[0052] (Operations)

[0053] In the information recording/reproducing apparatus, thesupporting/driving means 21 moves the objective lens 8 according to afocus error signal produced based on the outputs of the photodiodes 20 aand 20 b. The spot P2 is thus positioned on any of the tracks 24 on theguiding surface 16. Thereafter, the supporting drive unit 50 moves thecollimator lens 15 according to a focus error signal produced based onthe output of the photodiode 12. The spot P1 is thus positioned on theguiding surface 16.

[0054] Thereafter, the information recording/reproducing apparatus readsa track number of the track 24, on which the spot P2 is positioned,according to the outputs of the photodiodes 20 a and 20 b, and moves theobjective lens 8 towards the center of the disk according to the readtrack number. Consequently, the objective lens 8 is positioned so that,as indicated with imaginary lines, the optical axis of therecording/reproducing optical system will traverse the reference surface23 a and the spot P2 formed by the guiding optical system will spot thetrack 24.

[0055] Thereafter, the collimator lens 15 is moved so that the focuserror signal produced based on the output of the photodiode 12 will havea zero level. The spot P1 of recording/reproducing light is thuspositioned on the reference surface 23 a.

[0056] Consequently, as shown in FIG. 8, light reflected from thereflecting surface 58 a forms a small spot 60 on the receiving surface59 of the sensor 17. The receiving surface 59 is segmented into elevenportions, that is, receiving portions 59(1) to 59(11). A pitch betweenadjoining portions shall be p.

[0057] A signal is directly acquired at each of the receiving portions59(1) to 59(11) of the receiving surface 59. In addition, a subtracter62 provides a differential output signal [a-b] representing a differencebetween a signal a, which represents the sum of signals acquired at theodd-numbered receiving portions, and a signal b that represents the sumof signals acquired at the even-numbered receiving portions. Thedifferential output signal [a-b] has a zero level when the spot 60 islocated on the border between adjoining receiving portions. Thedifferential output signal [a-b] exhibits a sawtooth waveform whoseprogress is proportional to a length traveled by the spot 60.

[0058] When a current flows into the coils 57, the collimator lens 15 ismoved along the optical axis 18. This causes the reflecting surface 58 ato move along the optical axis 18, and causes the spot 60 to travel onthe receiving surface 59 along the optical axis 18. At what position onthe receiving surface the spot 60 is located is judged by detecting atwhich of the receiving portions 59(1) to 59(11), into which thereceiving surface is segmented, a signal of a different level isacquired. If the current flowing into the coils 57 is controlled so thatthe differential output signal [a-b] will have a zero level, the spot 60is positioned on the border between adjoining receiving portions. Theoutputs of the receiving portions 59(1) to 59(11) into which thereceiving surface is segmented may not be acquired. In this case, asufficiently large direct current is caused to flow into the coils 57,and the collimator lens 15 is moved to one end of a range of movement.The current is then reduced, and the number of times by which thedifferential output signal has a zero level is counted. Consequently, atwhat position the spot 60 is located can be judged from the count.

[0059] Moreover, a target level of the differential output signal [a-b]may not be zero but may be deviated by a predetermined magnitude fromthe zero level. Nevertheless, the position of the collimator lens 15,that is, the relative positions of the spots P1 and P2 in the directionsof the optical axes can be controlled finely.

[0060] Assume that the collimator lens 15 is moved by a lengthequivalent to the pitch p along the optical axis 18 towards the laserdiode 13. In this case, the position of the spot P2, which is formedthrough the objective lens 8, relative to the objective lens 8 in thedirection of the optical axis changes by a length Z1 determined with adepth magnification dependent on the collimator lens 15 and objectivelens 8. At this time, the position of the spot P1 relative to theobjective lens 8 in the direction of the optical axis remains unchanged.When the length Z1 is equal to the distance d between adjoiningrecording surfaces, the spot P2 is fixed to the guiding surface 16 dueto focus servo control. Consequently, the spot P1 is positioned on theside of the recording layer near the objective lens 8 while beingseparated by a length equivalent to the distance d from the spot P2.

[0061] Thereafter, the supporting drive unit 50 controls the position ofthe collimator lens 15 so as to retain an output of the sensor 17 at acertain level. Owing to this control, the position of the spot P2relative to the spot P1 in the direction of focus is held intact.

[0062] Thereafter, the objective lens 8 is moved in the direction oftracking, and the spot P2 is positioned on a desired track 24. Thus, theposition of the spot P2, which is formed by the guiding optical system,in the direction of tracking is controlled with a track 24 on theguiding surface 16 as a reference. Consequently, the position of thespot P1 formed by the recording/reproducing optical system is indirectlycontrolled in the direction of tracking.

[0063] The position of the objective lens 8 is controlled in thedirection of focus according to a focus error signal produced based onthe outputs of the photodiodes 20 a and 20 b. Consequently, the spot P2is held focused on any track 24 on the guiding surface 16. In otherwords, the spot P2 of guiding light is always positioned on the guidingsurface 16.

[0064] As mentioned above, the position of the collimator lens 15 iscontrolled in order to retain the output of the sensor 17 at a certainlevel. The position of the spot P2 relative to the spot P1 in thedirection of focus is therefore held intact, that is, the spot P2 isheld separated by a length equivalent to the distance d from the spot P1in the direction of focus. Consequently, the spot P2 is always locatedon a surface separated by the certain distance d from the guidingsurface 5.

[0065] This signifies that a surface on which information is recordedduring recording is exactly the recording surface 25 a separated by thedistance d from the guiding surface 16. Moreover, the spot P1 is alwayspositioned on the recording surface 25 a during reproduction. Theemployment of the information recording/reproducing apparatus enablesstable recording or reproduction.

[0066] Using the information recording/reproducing apparatus,information can be recorded or reproduced in or from the recordingsurface 25 b in the same manner as that in the recording surface 25 a.Specifically, first, the objective lens 8 is positioned so that theoptical axis 19 of the recording/reproducing optical system traversesthe reference surface 23 b and the spot P2 formed by the guiding opticalsystem spots a track 24 on the guiding surface 16. After the spot P1 ispositioned on the reference surface 23 b, the output of the sensor 17 isretained at a certain level so that the position of the spot P1 relativeto the spot P2 in the direction of focus will be held intact.Thereafter, the position of the spot P2 on the track 24 of the guidingsurface 16 is controlled in the direction of focus. Consequently, thespot P1 is positioned on the recording surface 25 b separated by thecertain distance 2 d from the guiding surface 16. The same applies torecording or reproducing of information in or from the recording surface25 c.

[0067] As seen from the above description, the informationrecording/reproducing apparatus can accurately and stably maintain therelative positions of the spots P1 and P2 despite various discouragingfactors that have caused the position of the spot P1 relative to thespot P2 in the direction of focus to change in the past. The factorsinclude a variation of the wavelength of light emanating from the laserdiode 1 or laser diode 13, a change in the sensitivity of thesupporting/driving means 21 to a driving current, and an offset erroroccurring in the sensor 17.

[0068] As mentioned above, the two parallel plate springs 52 areextended in the tangential direction. Referring to FIG. 1, thecollimator lens 15 is located in the center of a range of movement of ±1mm along the optical axis 18 with the plate springs 52 unloosened. Whenthe collimator lens 15 is seen from a direction perpendicular to thedirection of extension of the plate springs 52 shown in FIG. 1, theoptic axis of the collimator lens 15 is deviated by a distance d0 fromthe optical axis 18 of the optical system starting with the laser diode13 in a direction of its going apart from the plate springs 52.

[0069] As shown in FIG. 9, when the collimator lens 15 is moved alongthe optical axis, the movable ends of the plate springs 52, that is, thecollimator lens 15 is moved towards the stationary ends of the platesprings in the direction of extension of the springs.

[0070]FIG. 10 is a graph indicating the relationship between a length Zmoved along the optical axis by the collimator lens 15 and a length Dmoved in the direction of extension of the springs that is perpendicularto the optical axis. In this case, the length L of the springs in thedirection of extension thereof shall be 10 mm and a range of movementshall be ±1 mm.

[0071] Assume that the collimator lens 15 is located in the center ofthe range of movement along the optical axis and the optic axis of thecollimator lens 15 is aligned with the optical axis 18 with the platesprings 52 unloosened. According to the prior art, when the collimatorlens 15 is moved ±1 mm along the optical axis, the collimator lens 15 isalso moved 0.06 mm in the direction of extension of the plate springs52. Assuming that the focal length M of the collimator lens 15 is setto, for example, 12 mm, light emitted from the collimator lens 15travels while sloping 0.290° (=tan−1(0.06/12) in the tangentialdirection. The light then enters the objective lens 8 while sloping inthe tangential direction. Assuming that the focal length of theobjective lens 8 is 3 mm, the spot P2 is displaced by 15 μm (tan0.29×3)in the tangential direction.

[0072] In contrast, according to the present embodiment, as shown inFIG. 1, when the collimator lens 15 is located in the center of therange of movement with the plate springs 52 unloosened, the optic axisof the collimator lens 15 is deviated by a distance d0=0.03 mm from theoptical axis in a direction of its parting from the stationary ends ofthe springs. Therefore, even when the springs are unloosened, the opticaxis of the collimator lens 15 is deviated by 0.03 mm from the opticalaxis as seen from FIG. 10. Nevertheless, a maximum deviation of theoptic axis of the collimator lens 15 from the optical axis is 0.03 mmthat is a half of the one determined according to the prior art.Consequently, the slope of light emitted from the collimator lens 15 andthe length traveled in the tangential direction by the spot p2 arehalves of the ones determined according to the prior art.

[0073] In other words, despite small plate springs, a length moved alongthe direction of extension of the springs, which is perpendicular to adesired direction of movement, by an optical element can be minimized.In addition, a variation of the spot P2 caused by coma is minimized.This results in an information recording/reproducing apparatuscharacteristic of stable recording or reproducing.

[0074] Moreover, the direction of travel of the spot P2 is thetangential direction. A change in the relative positions of the spots P1and P2 in the direction of tracking is very small. Therefore, when thespot P2 is positioned on a track of the guiding surface, the spot P1will not be displaced from the recording track in the direction oftracking. Consequently, recording or reproducing can be achievedaccurately.

[0075] According to the present embodiment, a control means is includedfor controlling the position of the spot P1 relative to the spot P2 inthe direction of focus. However, no control means is included forcontrolling the position of the spot P1 relative to the spot P2 in thedirection of tracking. However, as mentioned above, when the position ofthe spot P1 relative to the spot P2 in the direction of focus ischanged, a change in the position of the spot P1 relative to the spot P2in the direction of tracking is very small. Consequently, recording orreproducing can be achieved accurately.

[0076] The optical element is not limited to the collimator lens but maybe the objective lens or laser diode. Moreover, a moving mechanism maybe a mechanism having magnets included in a movable assembly or amechanism including a bimetal. The optical element is supported anddriven in one direction along the optical axis of an optical systemincluding the optical element. Alternatively, the present embodiment maybe adapted to an apparatus in which the optical element is supported anddriven in two directions, that is, the direction of the optical axis andthe direction of tracking. Even in this case, even when the opticalelement is moved along the optical axis, the relative positions of lightspots formed through an objective lens in the direction of tracking donot change. The position of the optical element in the direction oftracking can therefore be controlled readily.

[0077] The present embodiment has been described on the assumption thatthe support member is realized with the plate springs capable ofelastically deforming. Alternatively, the support member may be a linkborne by a hinge made of a resin or the like. Furthermore, the presentembodiment can be adapted to an apparatus having a cantileveredsupporting mechanism or a both ends-fixed spring supporting mechanismhaving one end of a spring completely immobilized.

[0078] According to the present embodiment, the number of recordingsurfaces layered is three. Alternatively, the number of recordingsurfaces layered may only one or more than three. The arrangement ofoptical elements constituting an optical system may be replaced withanother arrangement, and the error detecting method may be replaced withanother method. Moreover, the present embodiment adopts the multilayerrecording method. The present invention is not limited to the recordingmethod but may be implemented in a single-layer recording method.

[0079] (Advantages)

[0080] As mentioned above, according to the present embodiment, amaximum (undesired) length moved in the direction of extension of theplate springs 52, which serve as a support member, by the collimatorlens 15 that is an optical element can be minimized. Consequently,recording or reproducing can be achieved with the relative positions oftwo light spots, which are formed on a recording medium through theobjective lens 8, in the direction of tracking held stable.

[0081] According to the present embodiment, the plate springs 52 servingas a support member for supporting the collimator lens 15 that is anoptical element are extended parallel to the recording surface of thedisk 9 (the surface of a recording medium). Light output from theoptical element is routed to the mirror 7 from the direction oftracking, and then routed to an objective lens. Therefore, when theoptical element is moved, the direction of extension of the springs forsupporting the optical element becomes parallel to the direction of therecording tracks of the moving recording medium. Consequently,displacements of a plurality of light spots in the direction of trackingthat is perpendicular to the direction of the recording tracks areminimized. A deviation of a light spot of recording light and/orreproducing light from a recording track is therefore minimized. Thisresults in an apparatus characteristic of stable recording orreproducing.

[0082] The optical system included in the informationrecording/reproducing apparatus in accordance with the presentembodiment may have optical elements thereof arranged as shown in FIG.11. Specifically, in a first variant of the optical system included inthe information recording/reproducing apparatus, light output from thecollimator lens 15 is routed to the mirror 7 from a direction that meetsthe recording tracks at an angle of 45°. At this time, the plate springs52 that support the collimator lens 15 are extended in a directionparallel to the disk 9.

[0083] According to the first variant, when the collimator lens 15 ismoved along the optical axis 18, the light spot P2 formed through theobjective lens 8 travels in a direction of arrow A that meets therecording tracks at the angle of 45°. Although the light spot P2 travelseven in the direction of tracking, the length traveled in the directionof tracking is equivalent to 1/{square root}2 of the length traveled inthe direction of arrow A. Although the length traveled by the light spotis larger than the one traveled by the spot formed by the optical systemshown in FIG. 1, the length traveled in the direction of tracking by thelight spot is smaller than the one traveled therein by the spot formedby the optical system shown in FIG. 1.

[0084] According to the first variant, the direction of travel of thelight spot on the disk 9 is a direction that meets the tracks at 45°.The angle at which the direction of travel meets the tracks may besmaller. The case where the angle is 0° refers to the aforesaidembodiment.

[0085] Moreover, the optical system included in the informationrecording/reproducing apparatus in accordance with the presentembodiment may have optical elements thereof arranged as shown in FIG.12. Specifically, in a second variant of the optical system included inthe information recording/reproducing apparatus, as shown in FIG. 12,light output from the collimator lens 15 is routed to the mirror 7 froma direction parallel to the recording tracks. At this time, the platesprings 52 that support the collimator lens 15 are extended in adirection perpendicular to the disk 9.

[0086] According to the second variant, when the collimator lens 15 ismoved along the optical axis 18, the light spot P2 formed through theobjective lens 8 travels in a direction of arrow B that is a directionparallel to the recording tracks. Consequently, the light spot P2 willnot travel in the direction of tracking.

[0087] Furthermore, the optical system included in the informationrecording/reproducing apparatus in accordance with the presentembodiment may have optical elements thereof arranged as shown in FIG.13. Specifically, in a third variant of the optical system included inthe information recording/reproducing apparatus, as shown in FIG. 13,light output from the collimator lens 15 is routed to the objective lens8 from a direction perpendicular to the recording tracks. At this time,the plate springs 52 that support the collimator lens 15 are extended ina direction parallel to the disk 9 and recording tracks alike.

[0088] According to the third variant, when the collimator lens 15 ismoved along the optical axis 18, the light spot P2 formed through theobjective lens 8 travels in a direction of arrow C that is a directionparallel to the recording tracks. Consequently, the light spot P2 willnot travel in the direction of tracking.

[0089] According to the present invention, it is apparent that a widerange of different embodiments can be formed based on the inventionwithout a departure from the spirit and scope of the invention. Thisinvention will be limited to the appended claims but not restricted toany specific embodiment.

What is claimed is:
 1. An optical element supporting device forinformation recording/reproducing apparatuses comprising: a light sourcefor irradiating a light beam; an objective lens through which the lightbeam irradiated from said light source forms at least one light spot ona recording medium; an optical element for routing the light beamirradiated from said light source to said objective lens; and a supportmember for supporting said optical element so that said optical elementcan move in a first direction, said support member being extended sothat when said optical element is moved in the first direction, theposition of the light spot in a direction of focus will be changed, andthe light spot will travel in a direction substantially parallel to therecording tracks of said recording medium.
 2. An optical elementsupporting device for information recording/reproducing apparatusesaccording to claim 1 , wherein said optical element is a collimatorlens.
 3. An optical element supporting device for informationrecording/reproducing apparatuses according to claim 1 , wherein thelight beam output from said optical element falls on a mirror from adirection of tracking, light reflected from the mirror falls on saidobjective lens, and said support member extends in a direction parallelto said recording medium.
 4. An optical element supporting device forinformation recording/reproducing apparatuses according to claim 1 ,wherein the light beam output from said optical element falls on amirror from a tangential direction, light reflected from the mirrorfalls on said objective lens, and said support member extends in adirection perpendicular to said recording medium.
 5. An optical elementsupporting device for information recording/reproducing apparatusesaccording to claim 1 , wherein the light beam output from said opticalelement falls on said objective lens from a direction perpendicular tosaid recording medium, and said support member extends in a directionparallel to said recording medium and in a tangential direction.
 6. Anoptical element supporting device for information recording/reproducingapparatuses comprising: a light source for irradiating a light beam; anobjective lens through which the light beam irradiated from said lightsource forms at least first and second light spots on a recordingmedium; an optical element for routing the light beam irradiated fromsaid light source to said objective lens; and a support member forsupporting said optical element so that said optical element can move ina first direction, said support member being extended so that when saidoptical element is moved in the first direction, the position of thesecond light spot relative to the first light spot in a direction offocus will be changed, and the second light spot will travel in adirection substantially parallel to the recording tracks of saidrecording medium.
 7. An optical element supporting device forinformation recording/reproducing apparatuses according to claim 2 ,wherein the light beam output from said optical element falls on amirror from a direction of tracking, light reflected from the mirrorfalls on said objective lens, and said support member extends in adirection parallel to said recording medium.
 8. An optical elementsupporting device for information recording/reproducing apparatusesaccording to claim 2 , wherein the light beam output from said opticalelement falls on a mirror from a tangential direction, light reflectedfrom the mirror falls on said objective lens, and said support memberextends in a direction perpendicular to said recording medium.
 9. Anoptical element supporting device for information recording/reproducingapparatuses according to claim 2 , wherein the light beam output fromsaid optical element falls on said objective lens from a directionperpendicular to said recording medium, and said support member extendsin a direction parallel to said recording medium and in a tangentialdirection.
 10. An optical element supporting device for informationrecording/reproducing apparatuses comprising: a light source forirradiating a light beam; an objective lens through which the light beamirradiated from said light source forms at least first and second lightspots on a recording medium, and which is supported by a support/drivemember so that the objective lens can move in two directions of adirection of focus and a direction of tracking; an optical element forrouting the light beam irradiated from said light source to saidobjective lens, said optical element being movable along an opticalaxis; and an optical element support member having said optical elementlocked in an opening of a holder, having one ends of two parallel platesprings fixed to the holder, having the other ends thereof fixed to afixture member, having a base fixed to the bottom of the fixture member,having yokes formed so that the yokes will sandwich the holder, havingmagnets, each of which is polarized in two directions, fixed to theinsides of the yokes, having coils opposed to the magnets, and having atarget fixed to the holder.
 11. An optical element supporting device forinformation recording/reproducing apparatuses according to claim 10 ,wherein said optical element is a collimator lens.
 12. An opticalelement supporting device for information recording/reproducingapparatuses according to claim 11 , wherein said collimator lens that ismoved along the optical axis by said support member has a positionthereof along the optical axis detected by a sensor.
 13. An opticalelement supporting device for information recording/reproducingapparatuses according to claim 12 , wherein said sensor is located onthe bottom of said base.
 14. An optical element supporting device forinformation recording/reproducing apparatuses according to claim 10 ,wherein said target has an opening that is shaped like an upper half ofa vertically elongated ellipse, receives light that is substantiallycollimated by said optical element, and transmits part of the lightemitted from said optical element, which enters the centralvertically-elongated portion of the elliptic opening, withoutintercepting it so that the part of the light will be routed to saidobjective lens.